Show Hints / Candidates will help you see the available pencil values within the cell, row, column, and boxes.

Sudoku How To Technique: Hidden Single

The second and ONLY OTHER method for entering a pencil value into a CELL, and almost as easy as the HIDDEN SINGLE method. This method uses the logic of “this is the only CELL that this HINT is available for within the CELL’s ROW, COLUMN, and BOX container”. Reviewing the diagram you can see that the cell R4C7 has the valid HINTS of {3,7,8}. However, the HINT of {8} is not present in any other CELL within its ROW R4. Knowing this knowledge, we know that CELL R4C7 is the only valid location for the PENCIL value of {8}. The highlighted value of {8} within the other cells would be removed after we enter the PENCIL value of {8} into R4C7.